VPA: bring k8s dependencies to v1.16.1

[wozniakjan]

The dependencies in VPA have been out of date for some time. This PR is trying to migrate go dep to go mod and upgrading k8s dependencies to v1.16.1.

This is branch is being used in kubernetes/kube-state-metrics#949 as an interim solution to test that PR but before merging, it would be ideal to point the dependencies back to this repo.

I am not entirely sure what I did is still desired - putting go modules to VPA sub directory, perhaps it would be better maintained at root directory. I tried to follow the layout set by go dep.

closes: #2447

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[bskiba]

✋ Looks like we worked on this simultaneously :) I'm working on getting #2486 merged. Will it will cover your needs as well?

[wozniakjan]

awesome, thanks! I believe it should cover everything the metrics-server needs, and I will test that later this week to make sure :)

Closing this in favor of #2486